1. Field of the Invention
This invention relates to a roller chain, and more particularly to a roller chain for conveyance wherein the frictional resistance of the chain itself is low for a long period of time and smooth running of the chain is realized to achieve a superior abrasion resistance and durability.
2. Description of the Related Art
Various roller chains are conventionally known, and a roller chain which is improved in frictional resistance between contact faces of a roller and a bushing is disclosed, for example, in Japanese Patent Laid-Open Publication No. (HEI) 4-78523. In the roller chain, grease is charged in a roller bearing disposed between a bushing and a roller so that the roller bearing and the grease may reduce the frictional resistance between contact faces of the roller and the bushing to achieve reduction of the frictional resistance against rotation and elongation of the life of rotation of the roller.
Another roller chain which is improved in frictional resistance between contact faces of a connection pin and a bushing is shown, for example, in FIG. 2 of Japanese Patent Laid-Open publiction No. (HEI) 9-14269. In the roller chain, a sintered oil-impregnated bushing is loosely fitted coaxially on a connection pin of a plate and a grease layer is formed at a bearing portion between the connection pin and the sintered oil-impregnated bushing. By a mutual action of lubricating oil impregnated in the sintered oil-impregnated bushing and the grease charged at the bearing portion, occurrence of an out-of-oil condition may be retarded to augment the life against friction between the connection pin and the sintered oil-impregnated bushing.
In such roller chains as described above, only the frictional resistance between contact faces of a bushing and a roller or between contact faces of a connection pin and a bushing is improved, but both of the frictional resistance between contact faces of a bushing and a roller and between contact faces of a connection pin and a bushing are not improved, and the life against friction as the entire roller chain cannot be achieved sufficiently.
In particular, while the former roller chain is improved in frictional resistance between contact faces of a bushing and a roller, it is not improved in frictional resistance between contact faces of a connection pin and a bushing, and the abrasion resistance and the durability of the entire chain are not sufficiently high. Further, the roller chain is subject to restriction in shape upon designing that a lubricant filling space for charging grease must be assured in a structure of the roller chain. Besides, as oil components of the grease are consumed, the grease becomes gradually solidified, resulting in increase in frictional resistance between the contact faces of the bushing and the roller. Consequently, the roller chain is disadvantageous in that the abrasion between the contact faces proceeds rapidly and this makes the roller chain fail to sufficiently exhibit a function of the roller chain itself.
On the other hand, with the latter roller chain, although it is improved in frictional resistance between contact faces of a connection pin and a bushing, since the improvement in frictional resistance between contact faces of a bushing and a roller, the abrasion resistance and the durability of the entire chain cannot be improved sufficiently. Further, since the connection pin and the bushing contact with and slide on each other by rocking motion over a fixed angle, the fluidity of the grease is low, and while a lubrication action functions with part of the grease which is present at the portions of the connection pin and the bushing at which they contact with and slide on each other and lubricant oozing out from the sintered oil-impregnated bushing, but the lubrication action does not function sufficiently at the other portions of the connection pin and the bushing at which they do not contact with and not slide on each other. Consequently, the roller chain is disadvantageous in that the life of the roller chain against abrasion is restricted by deterioration of the grease present at the portions of the connection pin and the bushing at which they contact with and slide on each other.